Drill and method for manufacturing cut product using same

ABSTRACT

A drill according to an embodiment of the present invention has a pair of main cutting edges positioned at a front end of a drill body, a pair of first chisel edges each extending from the pair of main cutting edges toward a rotation axis, and a second chisel edge positioned between the pair of first chisel edges and intersecting with the rotation axis of the drill body. When viewing a locus of rotation of the pair of first chisel edges and a locus of rotation of the second chisel edge in a cross section taken so as to include the rotation axis, the respective locus of rotation of the pair of first chisel edges have a rectilinear shape, and respective imaginary straight lines obtained by extending the locus of rotation of the pair of first chisel edges toward the rotation axis are positioned further to a rear end side of the drill body than the locus of rotation of the second chisel edge.

TECHNICAL FIELD

The present invention relates to a drill used for cutting and a methodfor manufacturing a cut product.

BACKGROUND

A drill disclosed in Japanese Unexamined Patent Application PublicationNo. 2004-34202A (Patent Document 1) is known as a drill conventionallyused for cutting a work material, such as a metal member and the like.In the drill disclosed in Patent Document 1, a part of a chisel edgesmoothly connected to a main cutting edge is removed by x-type thinningso that the drill has a second cutting edge that functions as a thinningcutting edge. According to this, as the cutting speed of the maincutting edge is faster than that of the chisel edge including thethinning cutting edge, chips generated by the chisel edge are pulled bychips generated by the main cutting edge. As a result, cracks aregenerated in the chips generated by the chisel edge, and it is thuspossible to fragment the chips into fine pieces.

In recent years, in such a case when a cutting tool is used for deephole drilling in which the depth of the drilled hole is large withrespect to the tool diameter, it is necessary to improve the durabilityof the cutting tool. Therefore, countermeasures, such as making the webthickness of the drill body thicker, have been considered. However, whenthe web thickness of the drill body is made thicker, the flute becomesshallower. As a result, the pulling force of the chips generated by themain cutting edge, which pulls the chips generated by the chisel edgeincluding the thinning cutting edge, becomes smaller. Thus, the chipsare less likely to be fragmented and tend to become long, and there is arisk that the chips may become clogged in the flute.

In light of the foregoing, an object of the present invention is toprovide a drill that is capable of fragmenting chips in a favorablemanner even when a web thickness of a drill body is made thicker.

SUMMARY OF THE INVENTION

A drill according to an embodiment of the present invention includes arod-shaped drill body caused to rotate around a rotation axis,

a pair of main cutting edges positioned in a front end portion of thedrill body,

a minor cutting edge that is positioned in the front end portion andconnects the pair of main cutting edges, and a pair of flutes that areprovided in an outer periphery of the drill body and extend in a spiralmanner around the rotation axis from the pair of main cutting edgestoward a rear end portion of the drill body. The minor cutting edge hasa pair of first chisel edges each extending from the pair of maincutting edges toward the rotation axis, and a second chisel edge that ispositioned between the pair of first chisel edges so as to intersectwith the rotation axis and that is shorter than each of the pair offirst chisel edges. When viewing a locus of rotation of the pair offirst chisel edges and a locus of rotation of the second chisel edge ina cross section taken so as to include the rotation axis, the locus ofrotation of the pair of first chisel edges has a rectilinear shape, andan imaginary straight line obtained by extending the locus of rotationof the first chisel edges toward the rotation axis is positioned furtherto a rear end side of the drill body than the locus of rotation of thesecond chisel edge.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a perspective view illustrating a drill according to a firstembodiment of the present invention.

FIG. 2 is a front view as viewed from a direction of a front end of thedrill illustrated in FIG. 1.

FIG. 3 is a simplified schematic view of a configuration of the drillillustrated in FIG. 2.

FIG. 4 is a side view of the drill illustrated in FIG. 2, as viewed froma direction A1.

FIG. 5 is a side view of the drill illustrated in FIG. 2, as viewed froma direction A2.

FIG. 6 is a side view illustrating an enlarged front end section of thedrill illustrated in FIG. 5.

FIG. 7 is a cross-sectional view of a cross section D1 of the drillillustrated in FIG. 5.

FIG. 8 is a cross-sectional view of a cross section D5 of the drillillustrated in FIG. 5.

FIG. 9 is a cross-sectional view of a cross section D2 of the drillillustrated in FIG. 2.

FIG. 10 is an enlarged cross-sectional view of a region B of the drillillustrated in FIG. 9.

FIG. 11 is a cross-sectional view of a cross section D3 of the drillillustrated in FIG. 2.

FIG. 12 is a cross-sectional view of a cross section D4 of the drillillustrated in FIG. 2.

FIG. 13 is a side view illustrating a modified example of the drillillustrated in FIG. 4.

FIG. 14 is a side view illustrating the drill illustrated in FIG. 13from a different direction.

FIG. 15 is a schematic view illustrating a helix angle of the drillillustrated in FIG. 13.

FIG. 16 is a perspective view illustrating a drill according to a secondembodiment of the present invention.

FIG. 17 is a front view as viewed from a direction of a front end of thedrill illustrated in FIG. 16.

FIG. 18 is an enlarged view of a region C of the drill illustrated inFIG. 17.

FIG. 19 is a perspective view illustrating one step of a method formanufacturing a cut product according to an embodiment of the presentinvention.

FIG. 20 is a perspective view illustrating one step of the method formanufacturing a cut product according to the embodiment of the presentinvention.

FIG. 21 is a perspective view illustrating one step of the method formanufacturing a cut product according to the embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

A drill according to each embodiment of the present invention will bedescribed below with reference to the appended drawings. However, forconvenience of explanation, each drawing referred to below onlyillustrates main constituent members of the respective embodiments,which are considered necessary for describing the present invention, ina simplified manner. Thus, the drill of the present invention may beprovided with a chosen configuration that is not illustrated in each ofthe drawings referred to in this specification. Further, dimensions ofthe members indicated in each of the drawings do not accuratelyrepresent dimensions of the actual configuration, dimension ratios ofrespective members, etc.

[Drill]

First, a drill 1 according to a first embodiment of the presentinvention will be described in detail with reference to FIGS. 1 to 12.

The drill 1 according to the first embodiment is provided with a drillbody 3, a pair of main cutting edges 5, a minor cutting edge 7, a pairof chip evacuation flutes 9 (hereinafter also simply referred to asflutes 9), and a pair of fluted land faces 11.

The drill body 3 has a rotation axis X and is configured so as to have arod-shape extending along the rotation axis X. The drill body 3 of thepresent embodiment is provided with a gripped portion 13, which iscalled a shank and gripped by a rotating spindle of a machining tool,and with a cutting portion 15 that is called a body and positioned on afront end side of the gripped portion 13. The gripped portion 13 is apart designed in accordance with a shape of the rotation axis X of themachining tool. The cutting portion 15 is a part that comes into contactwith a work material and plays a main role in cutting the work material.Note that an arrow Y1 in FIG. 1 indicates a rotational direction of thedrill body 3.

The pair of main cutting edges 5 are formed in a front end portion 3 aof the drill body 3, namely, in a front end section of the cuttingportion 15. Further, the minor cutting edge 7 is also formed in thefront end portion 3 a of the drill body 3. The minor cutting edge 7 ispositioned in the front end portion 3 a of the drill body 3 so as toconnect the pair of main cutting edges 5. The cutting of the workmaterial is performed by the pair of main cutting edges 5 and the minorcutting edge 7.

The pair of main cutting edges 5 according to the present embodiment areconfigured so as to be formed in a concavely curved-shape in a front endview. As a result, as it becomes easier to cause chips generated by thepair of main cutting edges 5 to be curled, it becomes easier to evacuatethe chips using the pair of flutes 9. Further, in order to improvecutting performance, the pair of main cutting edges 5 are provided sothat the locus of rotation of the pair of main cutting edges 5 are eachinclined with respect to the rotation axis X when the locus of rotationof the pair of main cutting edges 5 are viewed on a cross sectionincluding the rotation axis X.

The pair of main cutting edges 5 are positioned separately from eachother on either side of the minor cutting edge 7. The main cutting edges5 have 180 degree rotational symmetry with respect to a central axis ofthe drill body 3 in the front end view. The pair of main cutting edges 5have the rotational symmetry in this manner, thereby inhibiting wobblefrom occurring between the pair of main cutting edges 5 when the pair ofmain cutting edges 5 bite into the work material. Therefore, stable deephole drilling can be carried out. Note that, in this specification, thefront end view means viewing the drill 1 from a side of the front endportion 3 a of the drill body 3.

The pair of flutes 9 are provided on an outer periphery of the cuttingportion 15 in the drill body 3. Ends of the pair of flutes 9 on thefront end side are each connected to the pair of main cutting edges 5.The pair of flutes 9 extend around the rotation axis X in a spiralmanner from the pair of the main cutting edges 5 toward a rear end ofthe drill body 3. At this time, the pair of flutes 9 are formed only inthe cutting portion 15 and are not formed in the gripped portion 13, sothat the drill body 3 is gripped by the machining tool in a stablemanner.

The main purpose of the pair of flutes 9 is to evacuate the chipsgenerated by the pair of main cutting edges 5 and the minor cutting edge7. At the time of cutting, the chips generated by one main cutting edge5 a of the pair of main cutting edges 5 are evacuated to the rear endside of the drill body 3 through a flute 9 a of the pair of flutes 9,the flute 9 a being connected to the main cutting edge 5 a. Further, thechips generated by the other main cutting edge 5 b of the pair of maincutting edges 5 are evacuated to the rear end side of the drill body 3through a flute 9 b of the pair of flutes 9, the flute 9 b beingconnected to the main cutting edge 5 b.

Helix angles of the pair of flutes 9 of the present embodiment aredesigned so that the helix angle of the one flute 9 a becomes the sameas the helix angle of the other flute 9 b. Further, although the helixangles of the pair of flutes 9 of the present embodiment are eachdesigned so as to be constant from the front end to the rear end, thepresent invention is not necessarily limited to this type ofconfiguration. For example, the pair of flutes 9 may be configured tohave a plurality of helix angles as illustrated in FIGS. 13 to 15.

The pair of flutes 9 in a modified example illustrated in FIGS. 13 to 15are each provided with a first region 9 c, a second region 9 d, and athird region 9 e. The first region 9 c is positioned closest to thefront end side of the drill body 3 in the flute 9 and connected to themain cutting edge 5. The second region 9 d is positioned further to therear side of the drill body 3 than the first region 9 c. The thirdregion 9 e is positioned further to the rear side of the drill body 3and is positioned closest to the rear side of the drill body 3 in theentire flute 9. The ninth region 9 c has a helix angle α1, the secondregion 9 d has a helix angle α2, and the third region 9 e has a helixangle α3.

The respective helix angles of the pair of flutes 9 in the presentmodified example are not constant from the front end to the rear end.Specifically, as illustrated in FIG. 15, the helix angle α2 in thesecond region 9 d is smaller than the helix angle α1 in the first region9 c. Further, the helix angle α3 in the third region 9 e is larger thanthe helix angle α2 in the second region 9 d.

In the flute 9 in the present modified example, the first region 9 chaving the relatively large helix angle is positioned on the front endside of the cutting portion 15 so as to be connected to the main cuttingedge 5. Thus, the chips cut by the main cutting edge 5 do not remain inthe vicinity of the main cutting edge 5 and are promptly discharged tothe rear end side of the cutting portion 15. Further, the flute 9 in thepresent modified example is provided with the second region 9 d that ispositioned further to the rear end side of the cutting portion 15 thanthe first region 9 c. This configuration allows the chips, which arepromptly discharged from the first region 9 c, to be discharged furtherto the rear end side of the cutting portion 15. Further, as the secondregion 9 d has the relatively small helix angle α2, the rigidity of thedrill body 3 can be improved compared with a case in which the helixangle α2 and the helix angle α1 have the same value.

At this time, as the chips discharged from the second region 9 d aredistant from the first region 9 c, the flow of the chips is likely tostagnate. However, the flute 9 is provided with the third region 9 ethat is positioned further to the rear end side of the cutting portion15 than the second region 9 d and that has a relatively large helixangle. This configuration allows the chips, which are discharged fromthe second region 9 d to the third region 9 e, to be promptly evacuatedto the outside in the third region 9 e having the relatively large helixangle.

The helix angle α1 can be set to from 15 to 45 degrees, for example. Thehelix angle α2 can be set to from 3 to 20 degrees, for example. Thehelix angle α3 can be set to from 15 to 30 degrees, for example.

In the drill 1 of the present modified example, the helix angle α1 ofthe first region 9 c is set so as to be larger than the helix angle α3of the third region 9 e. The first region 9 c in the flute 9 isconnected to the main cutting edge 5, and the helix angle of the firstregion 9 c is the largest. As a result, a large pushing force is appliedto the chips at a stage when the chips are generated by the main cuttingedge 5, and allows chip-evacuation performance to be further improved.

The pair of flutes 9 in the present modified example are furtherprovided with a first connection region 17 and a second connectionregion 19 in addition to the first region 9 c, the second region 9 d,and the third region 9 e. The first connection region 17 is positionedbetween the first region 9 c and the second region 9 d. Specifically,the second region 9 d is connected to the first region 9 c via the firstconnection region 17. The helix angle in the first connection region 17changes smoothly from the front end side of the cutting portion 15toward the rear end side of the cutting portion 15. Thus, the secondregion 9 d is smoothly connected to the first region 9 c via the firstconnection region 17.

The second connection region 19 is positioned between the second region9 d and the third region 9 e. Specifically, the third region 9 e isconnected to the second region 9 d via the second connection region 19.The helix angle in the second connection region 19 changes smoothly fromthe helix angle α2 to the helix angle α3 from the front end side of thecutting portion 15 toward the rear end side of the cutting portion 15.Thus, the third region 9 e is smoothly connected to the second region 9d via the second connection region 19.

As the first region 9 c and the second region 9 d have different helixangles from each other, the flow direction of the chips changes in asection between the regions. Thus, in the section between the firstregion 9 c and the second region 9 d, the flow of the chips is likely tostagnate, and then the chips are likely to become clogged. However,having the first connection region 17 prevents the chips from becomingclogged in the section between the first region 9 c and the secondregion 9 d, which connects the regions smoothly.

Similarly, as the second region 9 d and the third region 9 e havedifferent helix angles from each other, the flow direction of the chipschanges in a section between the regions. However, having the secondconnection region 19, in the section between the second region 9 d andthe third region 9 e, which connects the regions smoothly, reduces therisk of the chips becoming clogged.

In the drill 1 of the present modified example, a length of the secondregion 9 d in the direction parallel to the rotation axis X is longerthan each of lengths of the first region 9 c and the third region 9 e inthe direction parallel to the rotation axis X. At the time of cutting, aload caused by the cutting is applied to the drill 1, and the cuttingportion 15 bends in some cases. In those cases, a central section of thecutting portion 15 is more likely to bend significantly compared with afront end section and a rear end section of the cutting portion 15.However, as securing the length of the second region 9 d in thedirection parallel to the rotation axis X to be relatively longer thanthe lengths of the first region 9 c and the third region 9 e, the secondregion 9 d having the relatively small helix angle and high rigidity,allows the cutting portion 15 to have good durability with respect tobending.

In the drill 1 of the present modified example, the length of the firstregion 9 c in the direction parallel to the rotation axis X is set to beapproximately from 10 to 20% of a length of the entire flute 9 in thedirection parallel to the rotation axis X. The length of the secondregion 9 d in the direction parallel to the rotation axis X is set to beapproximately from 30 to 40% of the length of the entire flute 9 in thedirection parallel to the rotation axis X. The length of the thirdregion 9 e in the direction parallel to the rotation axis X is set to beapproximately from 15 to 25% of the length of the entire flute 9 in thedirection parallel to the rotation axis X.

Note that as the flute 9 according to the present modified example hasthe first connection region 17 and the second connection region 19, thetotal of the above-described lengths of the first region 9 c, the secondregion 9 d, and the third region 9 e does not become 100% with respectto the length of the entire flute 9 in the direction parallel to therotation axis X.

Further, when the above-described length of the second region 9 d havingthe relatively small helix angle is longer than the above-describedlengths of the first region 9 c and the third region 9 e, each of whichhaving the relatively large helix angle, this configuration allows thelength of the entire flute 9 to be shortened without excessivelyimpeding the flow of the chips.

The cutting portion 15 according to the present embodiment is shaped byremoving sections corresponding to the pair of flutes 9, etc. from acolumn extending along the rotation axis X. A section of the cuttingportion 15, from which the pair of flutes 9 are removed, namely, asection positioned between the pair of flutes 9 forms fluted land faces11. The fluted land face 11 according to the present embodiment has amargin 11 a that is adjacent to the flute 9 on a rear side of arotational direction of the rotation axis X and a body clearance 11 bthat is adjacent to the margin 11 a on the rear side of the rotationaldirection of the rotation axis X.

On a cross-section that includes the rotation axis X and isperpendicular to the rotation axis X, the margin 11 a has an arc-shapepositioned on the same circle. A diameter of the circle corresponds toan outer diameter of the cutting portion 15. The body clearance 11 b isa surface formed so as to avoid friction between the outer periphery ofthe drill body 3 and a working surface while carrying out the cutting.Therefore, a distance of the body clearance 11 b from the rotation axisX is designed to be shorter than that of the margin 11 a so as to causea gap to be created between the body clearance 11 b and the workingsurface.

A depth V of the pair of flutes 9 can be set to be approximately from 10to 40% of the outer diameter of the cutting portion 15. Here, asillustrated in FIG. 7, the depth V of the flute 9 refers to a valueobtained by subtracting a distance from a bottom of the flute 9 to therotation axis X, on the cross section perpendicular to the rotation axisX, from a radius of the drill body 3. Thus, a diameter W of a webthickness, which is represented by a diameter of an inscribed circle onthe cross section perpendicular to the rotation axis X in the cuttingportion 15, is set to be approximately from 30 to 80% of the outerdiameter of the cutting portion 15. Specifically, when the outerdiameter of the cutting portion 15 is 20 mm, for example, the depth V ofthe flute 9 can be set to be approximately from 2 to 8 mm.

Note that the helix angle in the present embodiment refers to an angleformed between a leading edge (a leading edge of land) that is anintersection line formed by the flute 9 and the margin 11 a, and animaginary straight line that passes through a point on the leading edgeand is parallel to the rotation axis X.

In the drill 1 of the present embodiment, the outer diameter of thecutting portion 15 may be set to be from 6 to 42.5 mm, for example.Further, in the drill 1 of the present embodiment, when a length of anaxis line (a length of the cutting portion 15) is defined as L and adiameter (the outer diameter of the cutting portion 15) is defined as D,it is sufficient to set a relationship of L=3D˜12D.

A material of the drill body 3 may be a hard metal alloy containing WC(tungsten carbide) and Co (cobalt), where Co (cobalt) is a binder, analloy generated by adding additives such as TiC (titanium carbide) orTaC (tantalum carbide) to the above-described hard metal alloy, a metalsuch as stainless and titanium, or the like.

The cutting portion 15 according to the present embodiment has aconfiguration in which a part on the front end side, which includes thepair of main cutting edges 5, the minor cutting edge 7, a part of thepair of flutes 9, and a part of the pair of fluted land faces 11, can beattached to and removed from a part on the rear side.

The minor cutting edge 7 according to the present embodiment ispositioned in the front end section of the cutting portion 15 so as toconnect the pair of main cutting edges 5. The minor cutting edge 7 has apair of first chisel edges 21 and a second chisel edge 23. The pair offirst chisel edges 21 each extend from the pair of main cutting edges 5so as to become closer to the rotation axis X. Thus, the pair of firstchisel edges 21 each extend from the pair of main cutting edges 5 towardthe rotation axis X. The second chisel edge 23 connects the pair offirst chisel edges 21. Of the entire chisel edge formed by the pair offirst chisel edges 21 and the second chisel edge 23, the pair of firstchisel edges 21 function as a thinning edge.

Specifically, as illustrated in FIG. 2, when the drill body 3 is viewedfrom the front end, the second chisel edge 23 is positioned in a centralsection including the rotation axis X. Further, the pair of first chiseledges 21 are each positioned between both ends of the second chisel edge23 and the pair of main cutting edges 5. In the front end view, thesecond chisel edge 23 and the pair of first chisel edges 21 have 180degree rotational symmetry with respect to the rotation axis X of thedrill body 3, similarly to the pair of main cutting edges 5. The secondchisel edge 23 and the pair of first chisel edges 21 play a role incutting the work material along with the pair of main cutting edges 5.

As the cutting speed is slow in a central section around which the drill1 rotates, a larger cutting resistance is applied to the minor cuttingedge 7 than to the pair of main cutting edges 5. Thus, for the purposeof securing the strength of the cutting edges, when cut along animaginary plane including the rotation axis X, it is necessary to have alarge inclination angle of a locus of rotation of the minor cutting edge7 with respect to the rotation axis X.

At this time, because the first chisel edge 21 is formed by removing apart of the chisel edge by thinning, for example, an intersection anglebetween a cutting face and a flank of the pair of first chisel edges 21becomes smaller than an intersection angle between a cutting face and aflank of the second chisel edge 23. Thus, when the second chisel edge 23and the first chisel edges 21 are compared, the first chisel edges 21tend to have lower durability.

In the drill 1 of the present embodiment, when a locus of rotation X1 ofthe pair of first chisel edges 21 and a locus of rotation X2 of thesecond chisel edge 23 are viewed on the cross section including therotation axis X, the locus of rotation X1 of each of the first chiseledges 21 has a rectilinear shape. As a result, the strength of the firstchisel edges 21 is enhanced, and thus, the minor cutting edge 7 can havegood durability.

Further, each of imaginary straight lines obtained by extending each ofthe locus of rotations of the first chisel edges 21 toward the rotationaxis X is positioned closer to the rear end side of the drill body 3than the locus of rotation of the second chisel edge 23. Thisconfiguration suppresses the wobble generated when the pair of maincutting edges 5 and the minor cutting edge 7 bite into the workmaterial, while suppressing a deterioration in the durability of thefirst chisel edges 21. As a result, it becomes possible to cut the workmaterial in a favorable manner while enhancing the durability of theminor cutting edge 7.

Further, in the above-described cross sectional view, an inclinationangle θ2 with respect to the rotation axis X, of a locus of a section,on the locus of rotation X2 of the second chisel edge 23, which comesclose to the locus of rotation X1, is smaller than an inclination angleθ1 with respect to the rotation axis X, of the locus of rotation X1 ofthe pair of first chisel edges 21. This configuration allows the secondchisel edge 23 to bite into the work material in a favorable manner.

In the front end view, the pair of first chisel edges 21 according tothe present embodiment has not only a curved section, but also a linearsection 21 a, as illustrated in FIG. 3. The linear section 21 a issmoothly connected to the adjacent second chisel edge 23 and maincutting edge 5 via the curved section.

In recent years, in such a case when a cutting tool is used for deephole drilling in which a depth of a drill hole is large with respect tothe tool diameter, it is necessary to improve the durability of thecutting tool. Thus, as a countermeasure, it has been considered to makea web thickness of a drill body thicker, for example. In the presentembodiment, a drill with a thick web thickness refers to a drill havinga web thickness diameter that is from 0.3D to 0.5D with respect to thediameter D of the cutting portion 15, for example.

When the web thickness of the drill body 3 is made thicker, because theflutes 9 become shallower, the pair of main cutting edges 5 becomeshorter, and at the same time, the lengths of the pair of first chiseledges 21 and the second chisel edge 23 become longer. Thus, the pullingforce applied to the chips generated by the second chisel edge 23 andthe pair of first chisel edges 21 by the chips generated by the pair ofmain cutting edges 5 becomes weaker. As a result, as the chips are lesslikely to be fragmented and become longer, there is a risk that thechips may become clogged in the flutes 9.

However, because each of the imaginary straight lines obtained byextending each of the locus of rotations X1 of the first chisel edges 21toward the rotation axis X is positioned closer to the rear end side ofthe drill body 3 than the locus of rotation X2 of the second chisel edge23, the second chisel edge 23 ends up protruding toward the side awayfrom the rear end of the second chisel edge 23 beyond extended lines ofthe locus of rotation X1 of the first chisel edges 21. As a result ofcausing the second chisel edge 23 to protrude toward the side away fromthe rear end by creating an angle difference between point angles of thefirst chisel edges 21 and the second chisel edge 23 in this manner, thesecond chisel edge 23 and the first chisel edges 21 do not come intocontact with the work material continuously, but in a phased manner.

Thus, as a strain becomes large at a boundary between the chipsgenerated by the second chisel edge 23 and the chips generated by thefirst chisel edges 21, cracks are more likely to be generated in thechips generated by the second chisel edge 23. As a result, even when theweb thickness of the drill body 3 is made thicker, it is possible tofragment the chips in a favorable manner.

Further, in the front end view, when the first chisel edges 21 have thelinear section 21 a, the length of the pair of first chisel edges 21 caneach be shortened. Thus, even when the flutes 9 become shallower, thepair of main cutting edges 5 become shorter, and the length of the pairof first chisel edges 21 become longer, this configuration allowsdeterioration in the strength of the first chisel edges 21 to beminimized. As a result, even when the web thickness of the drill body 3is made thicker, it is possible to cut the work material in an even morefavorable manner while improving the durability of the minor cuttingedge 7.

Further, in the front end view, the second chisel edge 23 according tothe present embodiment has a linear section 23 a. The second chisel edge23 is positioned so as to include the rotation axis X when the drillbody 3 is viewed from the front end and is formed at a position closerto the rotation axis X than the pair of first chisel edges 21 and thepair of main cutting edges 5. Thus, although the pair of first chiseledges 21 and the pair of main cutting edges 5 perform the cutting insuch a way as to cut the work material, the second chisel edge 23 moreeasily performs the cutting in such a way as to crush the work material,as the cutting speed is relatively slow.

As the second chisel edge 23 performs the cutting in such a way as tocrush the work material in the above-described manner, a force isapplied from the work material to the second chisel edge 23 in adirection along the rotation axis X. In order to enhance durability withrespect to such a force, in the present embodiment, the second chiseledge 23 has the linear section 23 a as viewed from the front end. Havingthis type of the linear section 23 a enables the length of the secondchisel edge 23 to be shortened, and thus, the minor cutting edge 7 canhave good durability.

Further, in the front end view, imaginary straight lines extended fromboth ends of the linear section 23 a of the second chisel edge 23 eachintersect with the imaginary straight lines extended from the linearsection 21 a of the pair of first chisel edges 21. When the webthickness of the cutting portion 15 is made thicker, because the flutes9 become shallower, the pair of main cutting edges 5 become shorter, andat the same time, the lengths of the second chisel edge 23 and the firstchisel edges 21 become longer. Thus, the pulling force applied to thechips generated by the second chisel edge 23 and the first chisel edges21 by the chips generated by the main cutting edges 5 becomes weaker.Thus, there is a possibility that the chips are less likely to befragmented and become excessively long.

However, in the front end view, the second chisel edge 23 and the firstchisel edges 21 each have the linear sections 23 a and 21 a, and theimaginary straight lines extended along those sections intersect witheach other. Therefore, the strain becomes large at the boundary betweenthe chips generated by the second chisel edge 23 and the chips generatedby the first chisel edges 21, and thus, cracks are more likely to begenerated in the chips generated by the second chisel edge 23. As aresult, even when the web thickness of the cutting portion 15 is madethicker, this configuration is capable of fragmenting the chips in afavorable manner.

In a side view, on the second chisel edge 23, both end sections 23 bthat are connected to the pair of first chisel edges 21 are positionedfurther to the rear end side of the drill body 3 than a central section23 c that intersects with the rotation axis X. As a result of thecentral section 23 c of the second chisel edge 23 protruding toward theside away from the rear end, the section that intersects with therotation axis X in the second chisel edge 23 protrudes toward the sideaway from the rear end. This configuration can suppress the wobble,generated when the pair of main cutting edges 5 and the minor cuttingedge 7 bite into the work material.

Specifically, as illustrated in FIG. 6, the second chisel edge 23 hasthe central section 23 c that is shaped as a convexly curved surface ina side view from a direction perpendicular to the section of the secondchisel edge 23 intersecting with the rotation axis X. A central sectionof the convexly curved surface corresponds to the central section 23 cof the second chisel edge 23, and the central section of the convexlycurved surface is configured so as to protrude toward the side away fromthe rear end.

When the second chisel edge 23 is formed in a pointed shape toward theside away from the rear end, this pointed shape can suppress the wobble,generated when the minor cutting edge 7 bites into the work material.However, the durability of the second chisel edge 23 deteriorates.

In the drill 1 of the present embodiment, in a side view from adirection along the linear section of the second chisel edge 23, thecutting face and the flank of the second chisel edge 23 intersect witheach other at an acute angle. This configuration can suppress thewobble, generated when the minor cutting edge 7 bites into the workmaterial. In addition, in a side view from a direction perpendicular tothe linear section 23 a of the second chisel edge 23 and the rotationaxis X, as the second chisel edge 23 does not have an acutely angledshape, but is shaped as the convexly curved surface, the second chiseledge 23 can enjoy good durability while suppressing the above-describedwobble at the same time.

As already described above, the pair of main cutting edges 5 accordingto the present embodiment are configured so as to be formed in theconcavely curved shape in the front end view. In this way, when the pairof main cutting edges 5 have the concavely curved section, an angle θ3,at which a tangent of an end of the concavely curved section on the sideconnected to the first chisel edge 21 and the imaginary straight linealong the linear section 23 a in the second chisel edge 23 intersectwith each other, is preferably a right angle or an acute angle.

By this, a large strain tends to be generated in a section between thechips generated by the second chisel edge 23 and the chips generated bythe main cutting edges 5. The strain more easily causes cracks in thechips generated by the second chisel edge 23. The cracks can fragmentthe chips in a favorable manner.

At this time, the tangent of the end of a part of the concavely curvedsection in the pair of main cutting edges 5 connected to the firstchisel edge 21, and the imaginary straight line along the linear section21 a in the first chisel edge 21 preferably intersect with each other atan obtuse angle, and the imaginary straight line along the linearsection 21 a in the first chisel edge 21 and the imaginary straight linealong the linear section 23 a of the second chisel edge 23 preferablyintersect with each other at an obtuse angle.

Of the second chisel edge 23, the pair of first chisel edges 21, and thepair of main cutting edges 5, when adjacent cutting edge regionsintersect with each other at a right angle or an acute angle, a straingenerated in the chips becomes excessively large, and the chipsgenerated in the respective cutting edge regions may become fragmented.In this case, the cracks occurring in the chips generated by the secondchisel edge 23 do not spread to the chips generated by the pair of maincutting edges 5. This results in becoming difficult to fragment thechips generated by the pair of main cutting edges 5 in a favorablemanner.

However, the above-described configuration of the second chisel edge 23,the pair of first chisel edges 21, and the pair of main cutting edges 5make it easier to cause the cracks to occur in the chips generated bythe second chisel edge 23, and at the same time, to cause the cracksthat have occurred in the chips generated by the second chisel edge 23to spread to the chips generated by the pair of main cutting edges 5 ina favorable manner.

In the drill 1 of the present embodiment, an inclination angle θ4 of acutting face 25 a of the first chisel edge 21 is larger than aninclination angle θ5 of a cutting face 25 b of the second chisel edge 23with respect to an imaginary straight line parallel to the rotation axisX, and an inclination angle θ6 of a cutting face 25 c of the pair ofmain cutting edges 5 is larger than the inclination angle θ4 of thecutting face 25 a of the first chisel edge 21 with respect to theimaginary straight line parallel to the rotation axis X. In this way, ofthe cutting edge regions of the second chisel edge 23, the first chiseledge 21, and the main cutting edges 5, the cutting edge regions havelarger face angles as they are positioned further to the outer peripheryside of the drill body 3. As a result, it is possible to cause thecutting speed to become faster as the cutting edge regions arepositioned further to the outer peripheral side of the drill body 3.

By this, the chips generated by the second chisel edge 23 are moreeasily pulled by the chips generated by the first chisel edges 21, andfurther, the chips generated by the first chisel edges 21 are moreeasily pulled by the chips generated by the main cutting edge 5. As aresult, the cracks occur even more easily in the chips generated by thesecond chisel edge 23 and the first chisel edges 21, thereby enablingthe chips to be fragmented into finer pieces.

In order to cause the inclination angles of the cutting faces 25 b and25 c of the first chisel edge 21 and the main cutting edge 5 to belarger, a part of the cutting face 25 b of the first chisel edge 21 ispreferably positioned further to the rear side than the first chiseledge 21 in the rotational direction Y1, and at the same time, a part ofthe cutting face 25 c of the main cutting edge 5 is preferablypositioned further to the rear side in the rotational direction Y1 thanthe main cutting edge 5.

Further, the pair of flutes 9 in the drill 1 of the present embodimenthave substantially constant flute width and depth in their mainsections, except for sections which are positioned in rear ends of theflutes 9, where the flute depth becomes suddenly shallow, namely,sections in which the flutes are closed off.

When the width and depth of the flutes 9 are substantially constant inthis manner, as illustrated in FIG. 8, an imaginary straight line X3connecting central sections of the pair of fluted land faces 11 ispreferably perpendicular to the second chisel edge 23. In other words,when the drill 1 of the present embodiment is viewed as a perspectivefrom the front end, the imaginary straight line X3 connecting therespective central sections of the pair of fluted land faces 11, whichare positioned between the above-described rear ends in the pair offlutes 9, is preferably perpendicular to the linear section 23 a in thesecond chisel edge 23.

Note that FIG. 8 illustrates a cross section that is perpendicular tothe rotation axis X and that includes the rear ends in the main sectionsof the pair of flutes 9 in which the flute width and depth aresubstantially constant. Further, in FIG. 8, the main cutting edges 5 andthe minor cutting edge 7 are projected and illustrated as imaginarylines X4. Further, in the present specification, “being perpendicular”does not mean being strictly right-angled, but means being right-angledwith a tolerance of approximately from −5 to 5 degrees.

Further, as described above, the rear ends of the pair of flutes 9according to the present embodiment refers to the rear ends of the mainsections in which the flute width and depth are substantially constant.Therefore, the rear ends do not refer to the rear ends of the entireflutes 9, namely, the above-described rear ends in which the flute depthbecomes suddenly shallow.

When the cutting is performed using the drill 1, a load is likely to beapplied in the direction perpendicular to the linear section 23 a in thesecond chisel edge 23. Particularly, as the rear end section of thecutting portion 15, which is separated from the second chisel edge 23,is largely affected by the above-described load, a so-called chattervibration occurs originating from the above-described rear ends of thepair of flutes 9.

In general, the rigidity of the drill 1 on the cross section in thedirection perpendicular to the rotation axis X becomes largest withrespect to the direction connecting the respective central sections ofthe pair of fluted land faces 11. The imaginary straight line X3connecting the respective central sections of the pair of the flutedland faces 11 is perpendicular to the second chisel edge 23 in thesection largely affected by the above-described load, namely, at theabove-described rear ends of the pair of flutes 9. This configuration iscapable of improving durability against the above-described load and tosuppress the chatter vibration.

In the drill 1 of the present embodiment, the minor cutting edge 7 isformed by the above-described second chisel edge 23 and the pair offirst chisel edges 21, and the diameter W of the web thickness of thecutting portion 15 at the above-described rear ends of the pair offlutes 9 is formed to be larger than a chisel edge length of the secondchisel edge 23.

In this manner, with respect to the chisel edge length of the secondchisel edge 23, a sufficiently thick web thickness of the cuttingportion 15 is secured. Thus, even in such a case when a feed perrevolution of the drill 1 becomes large, the drill 1 is capable ofperforming the cutting in a stable manner.

Next, a drill 1 according to a second embodiment of the presentinvention will be described with reference to FIGS. 16 to 18. Note thatdifferent configurations of the drill of the present embodiment from thedrill according to the first embodiment will be described in detailbelow. Thus, when portions of the drill of the present embodiment arethe same as those of the drill of the first embodiment, the samereference numerals will be used and detailed descriptions will beomitted for those portions.

The drill 1 of the present embodiment is provided with the drill body 3,the pair of main cutting edges 5, the minor cutting edge 7, the pair offlutes 9, and the pair of fluted land faces 11 in the same manner as thedrill 1 of the first embodiment, as illustrated in FIG. 16. Further, theminor cutting edge 7 in the drill 1 of the present embodiment has thepair of first chisel edges 21 and the second chisel edge 23 in the samemanner as in the drill 1 of the first embodiment.

The pair of first chisel edges 21 in the first embodiment has the linearsection 21 a as viewed from the front end. Meanwhile, as illustrated inFIGS. 17 and 18, each of the first chisel edges 21 in the presentembodiment has a concavely curved section 21 b that is recessed towardthe rear side of the rotational direction of the rotation axis X asviewed from the front end. Specifically, each of the first chisel edges21 has the concavely curved section 21 b that is recessed further to therear side in the rotational direction of the rotation axis X, as viewedfrom the front end, than an imaginary straight line connecting anintersection point between the first chisel edge 21 and the secondchisel edge 23 and an intersection point between the first chisel edge21 and the main cutting edge 5.

As already described above, when each of the first chisel edges 21 hasthe linear section 21 a, even when the web thickness of the cuttingportion 15 is made thicker, the minor cutting edge 7 is capable ofhaving high durability. On the other hand, when each of first chiseledges 21 has the concavely curved section 21 b that is recessed towardthe rear side of the rotational direction of the rotation axis X asviewed from the front end, as described above, this configuration iscapable of enhancing the chip-evacuation performance.

Upon performing the cutting, when the first chisel edge 21 has theabove-described shape, the chips cut by the first chisel edge 21 arecurved according to the shape of the concavely curved section 21 b.Thus, the chips generated at ends of the first chisel edge 21 are pulledby the chips generated at a central section of the first chisel edge 21.Thus, the chips generated at the second chisel edge 23 adjacent to thefirst chisel edge 21 are pulled by the chips generated at the firstchisel edge 21.

As a result of the chips generated at the second chisel edge 23 beingpulled, cracks come more likely to occur in the chips generated by thesecond chisel edge 23 in the vicinity of the rotation axis X. Thosecracks are spread from the chips generated by the second chisel edge 23to the chips generated by the first chisel edges 21 and the chipsgenerated by the main cutting edges 5. Thus, the chips are fragmented,thereby enhancing the chip-evacuation performance.

When the pair of the main cutting edges 5 has a concavely curvedsection, as viewed from the front end, as in the drill 1 of the presentembodiment, a curvature of the concavely curved section 21 b in thefirst chisel edge 21 is preferably smaller than a curvature of theconcavely curved section in the main cutting edge 5 as viewed from thefront end. In this type of case, it is more likely that the pullingforce of the chips generated by the first chisel edges 21 that pulls thechips generated by the main cutting edges 5, becomes larger than thepulling force of the chips generated by the main cutting edges 5 thatpulls the chips generated by the first chisel edges 21. Therefore, thechips generated by the first chisel edges 21 can more easily flow intothe pair of flutes 9 connected to the pair of main cutting edges 5.

[Method for Manufacturing Cut Product]

Next, a method for manufacturing a cut product according to anembodiment of the present invention will be described while referring,as an example, to a case in which the drill according to theabove-described embodiments is used. The following describes the methodwith reference to FIGS. 19 to 21.

The method for manufacturing the cut product according to the presentembodiment is provided with steps from (1) to (4) described below.

(1) A step of arranging the drill 1 above a prepared work material 101(see FIG. 19).

(2) A step of causing the drill 1 to rotate around the rotation axis Xin the direction of the arrow Y1 and of causing the drill 1 to comecloser to the work material 101 in a direction Y2 (see FIGS. 19 and 20).

This step can be performed by fixing the work material 101 on a table ofa machining tool to which the drill 1 is attached and causing the drill1 to come closer to the work material 101 in a rotating state, forexample. Note that, at this step, it is sufficient if the work material101 and the drill 1 only move relatively closer to each other, so thework material 101 may be caused to come closer to the drill 1.

(3) A step of causing the pair of main cutting edges and the minorcutting edge of the rotating drill 1 to come into contact with a desiredposition on a surface of the work material 101 by causing the drill 1 tofurther get closer to the work material 101, and of forming a drilledhole (a through hole) 103 in the work material 101 (see FIG. 20).

At this step, from a viewpoint of obtaining a good finished surface, asetting is preferably made so that, of the cutting portion of the drill1, a part of the region on the rear end side of the drill 1 does notpenetrate through the work material 101. Specifically, as a result ofcausing the part of the region to function as a margin region for chipevacuation, excellent chip-evacuation performance via the region can beachieved.

(4) A step of separating the drill 1 from the work material 101 in adirection Y3 (see FIG. 21).

Also at this step, in the same manner as at the above-described step(2), it is sufficient if the work material 101 and the drill 1 arerelatively separated from each other, so the work material may be causedto be separated from the drill 1, for example.

By going through the above-described steps, excellent workability can beachieved.

Note that, in a case in which the above-described cutting of the workmaterial 101 is performed a plurality of times, and when a plurality ofthe drilled holes 103 are formed with respect to the one work material101, for example, it is sufficient to repeat the step of causing thepair of main cutting edges and the minor cutting edge of the drill 1 tocome into contact with different positions of the work material 101,while maintaining the rotating state of the drill 1.

Although some embodiments according to the present invention areillustrated above, the present invention is not limited to thoseembodiments. Needless to say, the present invention may be modified in adesired manner without departing from the scope of the invention.

For example, the shape of the cutting portion 15 is not limited to theconfiguration of the above-described embodiments, but othergenerally-used shapes can also be adopted. For example, the cuttingportion 15 may have a tapered shape in which the web thickness of theinscribed circle becomes thicker from the front end section toward therear end section. Further, the cutting portion 15 may have a drilldiameter (an outer diameter) that is inclined so as to become larger orsmaller from the front end section toward the rear end section.Furthermore, the cutting portion 15 may be provided with a so-calledundercut portion or a clearance portion.

Further, although in the above-described embodiments, the flute width ofthe pair of flutes 9 is constant from the front end side to the rear endside, alternatively, the flute width of the flutes 9 may become largeror smaller from the front end section toward the rear end section.Further, the flute widths of the pair of flutes 9 may be different fromeach other. Furthermore, the pair of flutes 9 may be formed to be joinedto each other by changing the helix angle of one of the pair of flutes 9or the helix angles of both of the pair of flutes 9.

Further, in the above-described embodiments, the drill 1 is describedthat is provided with the cutting portion 15 having a configuration inwhich a part including the front end can be attached to and removed froma part positioned on the rear end side. However, alternatively, thedrill 1 may have the cutting portion 15 formed by one member. Even inthis case, the same effects can be achieved as in the drill 1 accordingto the above-described embodiments.

REFERENCE NUMBER

-   1 Drill-   3 Drill body-   3 a Front end portion-   5, 5 a, 5 b Main cutting edge-   7 Minor cutting edge-   9, 9 a, 9 b Chip evacuation flute (flute)-   9 c First region-   9 d Second region-   9 e Third region-   11 Fluted land face-   11 a Margin-   11 b Body clearance-   13 Gripped portion-   15 Cutting portion-   17 First connection region-   19 Second connection region-   21 First chisel edge-   21 a Linear section-   21 b Curved section-   23 Second chisel edge-   23 a Linear section-   23 b Both end sections-   23 c Central section-   25 a, 25 b, 25 c Cutting face-   101 Work material-   103 Drilled hole

What is claimed is:
 1. A drill, comprising: a rod-shaped drill bodyrotatable around a rotation axis; a pair of main cutting edgespositioned on a front end portion of the drill body; a minor cuttingedge that is positioned on the front end portion and connects the pairof main cutting edges; and a pair of flutes that are disposed on anouter periphery of the drill body and extend in a spiral manner aroundthe rotation axis from the pair of main cutting edges toward a rear endportion of the drill body, the minor cutting edge comprising: a pair offirst chisel edges, each extending from the pair of main cutting edgestoward the rotation axis, and each comprising a first straight line; anda second chisel edge that; is positioned between the pair of firstchisel edges; intersects with the rotation axis; comprises a secondstraight line; and is shorter than the pair of first chisel edges, andin cross-section view, a first locus of rotation of the pair of firstchisel edges each comprises a single straight line and imaginarystraight lines obtained by extending the first locus toward the rotationaxis are positioned further to a rear end side of the drill body than asecond locus of rotation of the second chisel edge, wherein, in thefront end view, the second chisel edge is inclined with respect to thepair of the first chisel edges and the first straight line and thesecond straight line form an obtuse angle in the front end view.
 2. Thedrill according to claim 1, wherein the pair of first chisel edges eachcomprise a linear section in a front end view.
 3. The drill according toclaim 2, wherein the second chisel edge comprises a linear section inthe front end view.
 4. The drill according to claim 3, wherein, in thefront end view, imaginary straight lines obtained by extending both endsof the linear section of the second chisel edge respectively intersectwith imaginary straight lines obtained by extending the linear sectionsof the pair of first chisel edges.
 5. The drill according to claim 3,wherein both end sections of the second chisel edge, which are connectedto the pair of first chisel edges, are positioned further to the rearend side of the drill body than a central section of the second chiseledge, the central section intersecting with the rotation axis.
 6. Thedrill according to claim 5, wherein the second chisel edge is shaped asa convexly curved surface in a side view from a direction perpendicularto the rotation axis with respect to a section of the second chisel edgeintersecting with the rotation axis.
 7. The drill according to claim 3,wherein, in the front end view, the pair of main cutting edges eachcomprise a concavely curved section, and a tangent of an end of theconcavely curved section on a side connected to the first chisel edgeintersects at an acute angle with an imaginary straight line obtained byextending the linear section of the second chisel edge.
 8. The drillaccording to claim 1, wherein the flute comprises a first region that ispositioned on a front end side of the drill body and comprises a helixangle α1, a second region that is positioned further to a rear end sideof the drill body than the first region and comprises a helix angle α2that is smaller than the helix angle α1, and a third region that ispositioned further to the rear end side of the drill body than thesecond region and comprises a helix angle α3 that is larger than thehelix angle α2.
 9. The drill according to claim 8, wherein the helixangle α1 is larger than the helix angle α3.
 10. The drill according toclaim 8, wherein the second region is connected to the first region viaa first connection region in which a helix angle smoothly changes fromthe helix angle α1 to the helix angle α2 from the front end side of thedrill body toward the rear end side of the drill body, and the thirdregion is connected to the second region via a second connection regionin which a helix angle smoothly changes from the helix angle α2 to thehelix angle α3 from the front end side of the drill body toward the rearend side of the drill body.
 11. The drill according to claim 8, whereina length of the second region in a direction parallel to the rotationaxis is longer than each of lengths of the first region and the thirdregion in the direction parallel to the rotation axis.
 12. A method formanufacturing a cut product, comprising: causing a drill described inclaim 1 to rotate around the rotation axis; causing the pair of maincutting edges and the minor cutting edge of the drill to come intocontact with a work material; and separating the drill from the workmaterial.